The present invention generally relates to hydraulic coupler devices, such as those used in connection with aviation fuel service. More particularly, the present invention relates to a hydraulic coupler that is designed to break away from a fluid hydrant when experiencing an excessive external pull or load.
The Energy Institute and the American Petroleum Institute (EI and API) provides specifications which outline the requirements for products intended for equipment used in aviation turbine fuel service or for products used in the process of fueling aircraft. Prior to 2001, the specifications had a requirement for hydrant couplers where the coupler had to be able to withstand a pull force of two thousand pounds without breaking or decoupling from the hydrant pit valve. There was no requirement that the coupler break away. The intent of this original requirement was to simulate a possible condition where the coupler would be connected to a system piping and the fueling truck would either drive away or run into the coupler while it was connected. The two-thousand-pound pull test verified that the coupler could withstand the possibility of such an incident.
In 2001, the EI and API specifications were revised such that at an excessive pull force between 4,000-5,000 pounds the coupler was required to break away from the pit valve hydrant without damaging the hydrant or preventing the pit valve from closing. Requiring breakaway is intended to prevent fuel spillage into the fueling vault and/or onto the airport tarmac and minimize the potential for damaging underground piping, as repairing underground piping is considered more costly and time consuming than replacing a hydrant.
A breakaway coupler exists wherein the locking mechanism includes notched latching lugs. The notched latching lugs grip a flange of the pit valve hydrant to secure the two components together during a fueling operation. These notches create high stressed concentrated areas on the latch that can predictably break under given load conditions. Although this breakaway design works, the notches on the lug latches are directly loaded against all internal pressure forces as well as external physical forces. The notches can fatigue over time, which weakens the breakaway feature such that over time it has the potential of breaking away at less than the required external load force. This direct loading from internal fluid pressure results in higher forces acting on the latches which can contribute to a shorter fatigue life, requiring that the wear or condition of the latches be closely monitored. To avoid the potential for breakaway at a lower than desired load force, the notched latches should be periodically inspected and/or replaced. Since all of the latches are notched, this requires that each individual latch be stressed. Manufacturing variations in the notch detail of the latches can result in variations in the strength of each latch, which varies the failure load force value. Couplers currently in the marketplace use eight or more latches on their couplers and, given the nature of the type of breakaway design with multiple components of failure, could make the actual breakaway pull force of the coupler difficult to predict. Manufacturing processes are critical to ensure the material and dimensional details of the individual latches are consistent for each coupler assembly.
Accordingly, there is a continuing need for a breakaway hydraulic coupler which will reliably break away from a fluid hydrant at the desired minimum load force, does not have a shorter fatigue life due to being directly loaded against all internal pressure and external physical forces, and which will have a predictable breakaway load force. The present invention addresses these needs, and provides other related advantages.